40k is almost a decade older.
main argument of 40k fans, and myself, is that games workshop had a contract with blizzard, for a 40k based computer game. it was still in the making, and GW had to cancel the contract. blizzard didnt want to let their work be wasted, and continued with work. they had to tweak human faction a bit, to turn eldar into protoss and tyranids into zerg, and starcraft was born!

many zerg units even look the same like their tyranid ancestors (zerglings and hydralisks mainly). thats why many 40k fans absolutely hate starcraft.
i mean, on one side we have god emperor and horus, 2 almost immortal demigods fighting eachother, and on the other we have mengsk and the evil guys, with mengsk becoming a bad guy in the sequel. PLEASE.
if they wanted to copy 40k, they should at least leave its epicness intact.